Implementing 70% of the most basic of all functionality of Excel is easy. Implementing 90% is insanely difficulty.
I would say Handsontable reaches the mark of 78%.
I've tried twice, one with React + Mori and one in Cyclejs. In the first I may have reached 82%, in the second probably 85%. But in both cases the latest features I added started to conflict with the oldest ones and I abandoned everything.